From: Peter Zijlstra Date: Sun, 14 Jan 2018 10:27:13 +0000 (+0100) Subject: x86,perf: Disable intel_bts when PTI X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=99a9dc98ba52267ce5e062b52de88ea1f1b2a7d8;p=openwrt%2Fstaging%2Fblogic.git x86,perf: Disable intel_bts when PTI The intel_bts driver does not use the 'normal' BTS buffer which is exposed through the cpu_entry_area but instead uses the memory allocated for the perf AUX buffer. This obviously comes apart when using PTI because then the kernel mapping; which includes that AUX buffer memory; disappears. Fixing this requires to expose a mapping which is visible in all context and that's not trivial. As a quick fix disable this driver when PTI is enabled to prevent malfunction. Fixes: 385ce0ea4c07 ("x86/mm/pti: Add Kconfig") Reported-by: Vince Weaver Reported-by: Robert Święcki Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Cc: Alexander Shishkin Cc: greg@kroah.com Cc: hughd@google.com Cc: luto@amacapital.net Cc: Vince Weaver Cc: torvalds@linux-foundation.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180114102713.GB6166@worktop.programming.kicks-ass.net --- diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c index 141e07b06216..24ffa1e88cf9 100644 --- a/arch/x86/events/intel/bts.c +++ b/arch/x86/events/intel/bts.c @@ -582,6 +582,24 @@ static __init int bts_init(void) if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts) return -ENODEV; + if (boot_cpu_has(X86_FEATURE_PTI)) { + /* + * BTS hardware writes through a virtual memory map we must + * either use the kernel physical map, or the user mapping of + * the AUX buffer. + * + * However, since this driver supports per-CPU and per-task inherit + * we cannot use the user mapping since it will not be availble + * if we're not running the owning process. + * + * With PTI we can't use the kernal map either, because its not + * there when we run userspace. + * + * For now, disable this driver when using PTI. + */ + return -ENODEV; + } + bts_pmu.capabilities = PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE | PERF_PMU_CAP_EXCLUSIVE; bts_pmu.task_ctx_nr = perf_sw_context;